1. Field of the Invention
This invention relates to thermoelectric modules having endothermic properties for absorbing heat from electronic components and the like.
2. Description of the Related Art
A conventional example of a thermoelectric module comprising an upper substrate 2 and a lower substrate 1 will be described with reference to FIGS. 6 to 9, wherein FIG. 6 is a plan view showing the upper substrate 2, FIG. 7 is a right side view, FIG. 8 is a front view, and FIG. 9 is a plan view showing the lower substrate 1. The upper substrate 2 and the lower substrate 1, both of which are made of alumina, are arranged opposite to each other with a prescribed space therebetween, in which upper electrodes 5 are arranged on the upper substrate 2, and lower electrodes 6 are arranged on the lower substrate 1. The upper electrodes 5 and the lower electrodes 6 are alternately arranged to sandwich different types of thermoelectric elements 3 therebetween. Specifically, p-type thermoelectric elements and n-type thermoelectric elements are alternately arranged between the upper electrodes 5 and the lower electrodes 6 except a leftmost lower electrode 6a. A single n-type thermoelectric element is only arranged for the leftmost lower electrode 6a, which is connected with a lead 7. In FIGS. 6 to 9, symbols of arrows show directions of currents flowing through the thermoelectric module. That is, a current flows through the leftmost lower electrode 6a (see FIG. 8), from which the current flows into the upper electrode 5 via the n-type thermoelectric element; and then, the current flows into the lower electrode 6 adjoining the leftmost lower electrode 6a via the p-type thermoelectric element. As described above, the current sequentially flows through the lower electrode 6, n-type thermoelectric element 3, upper electrode 5, p-type thermoelectric element 3, and lower electrode 6 in turn. Due to the Peltier effect, heat is extracted from the upper substrate 2 and is then transferred to the lower electrode 1. Therefore, an electronic component mounted on the surface of the upper substrate 2 is cooled, so that heat is radiated from the lower substrate 1. Both the upper electrodes 5 and the lower electrodes 6 have the same thickness, which ranges from 50 μm to 100 μm, for example.
In the case of a thermoelectric module having a relatively large maximal endothermic value Qcmax, a current flowing through electrodes may become large and range from 5A to 10A, for example. This causes great heating values at electrodes, which may deteriorate performance of the thermoelectric module.
Incidentally, the maximal endothermic value Qcmax is defined with respect to a thermoelectric module having a heat absorbing side and a heat radiating (or emitting) side, wherein it is determined as an endothermic value that is produced when a difference between temperature (Tc) of the heat absorbing side, on which a heater is mounted, and temperature (Th) of the heat radiating side becomes zero (i.e., 0° C., where Th=Tc=27° C., for example).